1. Technical Field
The present disclosure relates to a fuel cell system including a desulfurizer that removes a sulfur compound in a raw material supplied to a fuel cell unit, a purifier that removes carbon monoxide in combustion exhaust gas emitted from the fuel cell unit, and a heat exchanger that performs heat exchange of air supplied to the fuel cell unit and the combustion exhaust gas.
2. Description of the Related Art
Conventionally, a fuel cell system has high efficiency of electric-power generation even when the fuel cell system is small in size. Thus, the fuel cell system is utilized as an electric-power generator in a distributed electric-power generation system. Typical examples of a raw material supplied to the fuel cell system include natural gas (urban gas), liquefied petroleum gas (LPG), gasoline, and kerosene, which are supplied from already-existing infrastructures.
The raw material described above includes, for example, a sulfur compound that serves as an odorant for detecting a gas leak or a sulfur compound that originates from the raw material. Such sulfur compounds poison a reforming catalyst for reforming the raw material and an electrode catalyst of a fuel cell, and decrease performance of the catalysts. Thus, the fuel cell system is provided with a desulfurizer that removes the sulfur compound in the raw material.
The desulfurization performance of some desulfurization catalysts for the desulfurizer depend on temperatures. Examples of such desulfurization catalysts include a hydrodesulfurization catalyst that is used in a hydrodesulfurization process and an absorbent desulfurization catalyst that exerts high activity at high temperatures. To increase the desulfurization performance of such desulfurization catalysts, each desulfurization catalyst needs to be heated to a temperature suitable for the desulfurization catalyst. Thus, a fuel cell system (a solid oxide fuel cell system), where the desulfurizer is heated with exhaust heat emitted from the fuel cell or the reformer, such as radiant heat or transferred heat, is proposed (see, for example, Japanese Patent No. 5507119 regarding the hydrodesulfurization and Japanese Unexamined Patent Application Publication No. 2013-191280 regarding the absorbent desulfurization).
A fuel cell system (a solid oxide fuel cell system), where fuel not utilized in electric-power generation of a fuel cell is combusted and the combustion heat is used to heat a desulfurizer, is also proposed. In this case, the combustion exhaust gas caused when the fuel is combusted includes carbon monoxide. Thus, a combustion catalyst that brings the carbon monoxide into oxidative decomposition before the combustion exhaust gas is emitted to the outside is provided in the fuel cell system (see, for example, Japanese Patent No. 5584507).
However, conventional techniques described in above-mentioned Japanese Patent No. 5507119, Japanese Unexamined Patent Application Publication No. 2013-191280, and Japanese Patent No. 5584507 are still susceptible to improvement in view of a quest for further increase in the efficiency and reliability of the fuel cell system.